1. Field of the Invention
The present invention relates to an organic light emitting display and a driving method thereof.
2. Description of the Related Art
An organic light emitting display is a next-generation flat type display that has a relatively thin thickness, wide viewing angle and rapid response time.
Referring to FIG. 1, an organic light emitting diode (OLED) of an organic light emitting display is composed of an anode (ITO), an organic thin film and a cathode (metal). The organic thin film is composed of a multilayer structure including an emission layer, an electron transport layer (ETL) and a hole transport layer (HTL), and the multilayer structure may further include a separate electron injecting layer (EIL) and a hole injecting layer (HIL).
The organic light emitting display controls the brightness of each pixel and displays images by controlling the amount of current flowing into the organic light emitting diode (OLED) of each pixel. That is, the current corresponding to the data voltage is supplied to the OLED, and then the OLED emits light according to the supplied current. Here, the applied voltage can have various levels within a specific range to express a gradation.
Generally, self-emitting displays are devices for self-emitting light when the electric energy or other energies are supplied. Examples of a self-emitting display include a light emitting diode (LED) display, a cathode ray tube (CRT) display, a plasma display panel (PDP), an electroluminescence (EL) display, a field emission display (FED) and so on.
Self-emitting displays are widely used, because that they offer excellent visibility in low-light conditions, and their manufacturing methods are usually simpler than a non-self-emitting display, such as a liquid crystal display (LCD). In addition, the self-emitting display consumes relatively less power. However, there is a disadvantage in that the visibility of these displays, in a case where external light is great, is considerably lower than that of a reflective liquid crystal display, and thus it is problematic to use them in high-light conditions.
In particular, mobile displays provided with an active matrix organic light emitting display (AMOLED) are often displayed in the outdoor, and therefore the mobile displays with the AMOLED have to solve the problem of low visibility in the outdoor. That is, the display element of the AMOLED should be relatively bright when it is turned on in order to have proper visibility under strong external light. Otherwise, the contrast ratio is considerably reduced and thus the visibility is degraded.
However, a method, which always turns on the display element brightly, result in that power consumption is high and more current flows into the organic light emitting diode OLED, and therefore there is a problem in that the lifespan of the organic light emitting diode OLED is reduced.